The invention concerns an integrated circuit that has control units for controlling the threshold potentials of its transistors.
A circuit of this kind is described in U.S. Pat. No. 5,874,851. Because of fluctuations in the process of manufacturing integrated circuits, the transistors of the integrated circuit are subject to parameter fluctuations. According to U.S. Pat. No. 5,874,851, the threshold potentials of the field effect transistors must be controlled in order to compensate for the fluctuations. In this way it is possible to compensate both the process fluctuations arising during manufacture and also the temperature effects occurring during operation of the circuit. In the solutions described in U.S. Pat. No. 5,874,851, control of the potential of the n-well is exercised independently of control of the potential of the p-well.
Since most subcircuits of an integrated circuit include both n-channel transistors and p-channel transistors, the function of such a subcircuit is dependent on the threshold potentials of both types of transistor. Because every control has a specific transient response, it can occur with the independent control of the threshold potentials of the two transistor types as described in U.S. Pat. No. 5,874,851, that the transient response of the two controls or their response to interferences can have different chronological characteristics. However, this exerts influences on the functioning of the subcircuit.
It is accordingly an object of the invention to provide an integrated circuit with control of the threshold potentials of its transistors that overcomes the above-mentioned disadvantages of the prior art devices of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, an integrated circuit containing first transistors of a first conductivity type having a first threshold potential and substrate terminals for receiving a first substrate potential. Second transistors of a second conductivity type having a second threshold potential and substrate terminals for receiving a second substrate potential are also provided. A first control unit is connected to the first transistors for controlling the first threshold potential. The first control unit has a first input for a required value of the first threshold potential, a second input for an actual value of the first threshold potential, and an output connected to the substrate terminals of the first transistors. A second control unit is connected to the second transistors for controlling the second threshold potential. The second control unit has a first input receiving a required value of the second threshold potential, a second input receiving an actual value of the second threshold potential, and an output connected to the substrate terminals of the second transistors. The required value of the second threshold potential is proportional to the actual value of the first threshold potential of the first transistors.
In the integrated circuit according to the invention a first control unit serves for controlling the threshold potential of the transistors of the first conductivity type and a second control unit serves for controlling the threshold potentials of transistors of the second conductivity type. The second control unit is supplied with a required value for the threshold potential of the transistors of the second conductivity type, which is proportional to the contribution to the required value of the threshold potential of the transistors of the first conductivity type. Thus the control of the threshold potential of the transistors of the second conductivity type is a control which is dependent on the control through the first control unit. In this way it is achieved that the threshold potential of the transistors of the second conductivity type is modified in dependence of the threshold potential of the transistors of the first conductivity type. This in turn achieves alignment of the chronological behavior of the two control units. Since the relationship of the threshold potentials of the transistors of different conductivity types influences the switching characteristics of subcircuits containing transistors of both conductivity types (both the digital switching characteristics and the analog amplification in the case of subcircuits which perform an amplifying function), it is achieved through the invention that these switching characteristics are independent of fluctuations in process parameters during the manufacture of the integrated circuit or of disturbances arising during their operation.
The switching characteristics of a subcircuit are essentially dependent on the saturation currents flowing in the transistors it contains. These currents depend on the threshold potential of the transistors. The switching speed and the working symmetry of such kinds of subcircuit are especially dependent on the relationship of the threshold potentials of the different types of transistor. As a result of the invention, both the switching speed and also the working symmetry (i.e. the switching characteristics) of the integrated circuit become independent of interfering influences.
The integrated circuit can, for example, contain a differential amplifier that includes transistors of both conductivity types. The relationship of the threshold potentials of the transistors is especially relevant for the way in which differential amplifiers function.
In accordance with an added feature of the invention, a first supply terminal and a second supply terminal are provided. The second control unit has a third transistor of the first conductivity type with a controllable path, a first terminal, a second terminal and a gate terminal. The gate terminal of the third transistor is connected to the second terminal of the third transistor. The second control unit has a fourth transistor of the second conductivity type with a controllable path, a gate terminal, a first terminal, and a second terminal. The controllable path of the third transistor and the controllable path of the fourth transistor are disposed in a series circuit between the first supply terminal and the second supply terminal. The gate terminal of the fourth transistor is connected to the second terminal of the fourth transistor. A comparison unit is provided and has a first input connected to a circuit node between the controllable path of the third transistor and the controllable path of the fourth transistor and a second input receiving a comparison value. The comparison unit has an output and generates an output signal. A generator is connected to the output of the comparison unit and outputs the second substrate potential for the second transistors. The generator generates the second substrate potential in dependence on the output signal from the comparison unit.
With the foregoing and other objects in view there is further provided, in accordance with the invention, an integrated circuit containing a first supply terminal, a second supply terminal, and a differential amplifier. The differential amplifier includes a first transistor of a first conductivity type and has a controllable path, a gate terminal, a substrate terminal for receiving a first substrate potential, and a first threshold potential; a second transistor of the first conductivity and has a controllable path, a gate terminal, a substrate terminal for receiving the first substrate potential, and the first threshold potential; and a third transistor of a second conductivity type and has a controllable path, a gate terminal, a substrate terminal for receiving a second substrate potential, and a second threshold potential. The controllable path of the first transistor and the controllable path of the third transistor are disposed in series between the first supply terminal and the second supply terminal. A fourth transistor of the second conductivity type is provided and has a controllable path, a gate terminal, a substrate terminal for receiving the second substrate potential, and the second threshold potential. The controllable path of the second transistor and the controllable path of the fourth transistor are disposed in series between the first supply terminal and the second supply terminal. A first signal input terminal is connected to the gate terminal of the first transistor and to the gate terminal of the third transistor. The first signal input terminal is further connected to a circuit node between the second transistor and the fourth transistor. A second signal input terminal is connected to the gate terminal of the second transistor and to the gate terminal of the fourth transistor. The second signal input terminal is further connected to a circuit node between the first transistor and the third transistor. A first control unit for controlling the first threshold potential of the first transistor and the second transistor is provided. The first control unit has a first input for a required value of the first threshold potential, a second input for an actual value of the first threshold potential, and an output connected to the substrate terminal of each of the first transistor and the second transistor. A second control unit for controlling the second threshold potential of the third transistor and the fourth transistor is provided. The second control unit has a first input receiving a required value of the second threshold potential, a second input receiving an actual value of the second threshold potential, and an output connected to the substrate terminal of each of the third transistor and the fourth transistor. The required value of the second threshold potential is proportional to the actual value of the first threshold potential.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an integrated circuit with control of the threshold potentials of its transistors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.